Oxygen-sensing reporter strain of Pseudomonas fluorescens for monitoring the distribution of low-oxygen habitats in soil.

The root-colonizing bacterium Pseudomonas fluorescens CHA0 was used to construct an oxygen-responsive biosensor. An anaerobically inducible promoter of Pseudomonas aeruginosa, which depends on the FNR (fumarate and nitrate reductase regulation)-like transcriptional regulator ANR (anaerobic regulation of arginine deiminase and nitrate reductase pathways), was fused to the structural lacZ gene of Escherichia coli. By inserting the reporter fusion into the chromosomal attTn7 site of P. fluorescens CHA0 by using a mini-Tn7 transposon, the reporter strain, CHA900, was obtained. Grown in glutamate-yeast extract medium in an oxystat at defined oxygen levels, the biosensor CHA900 responded to a decrease in oxygen concentration from 210 x 10(2) Pa to 2 x 10(2) Pa of O(2) by a nearly 100-fold increase in beta-galactosidase activity. Half-maximal induction of the reporter occurred at about 5 x 10(2) Pa. This dose response closely resembles that found for E. coli promoters which are activated by the FNR protein. In a carbon-free buffer or in bulk soil, the biosensor CHA900 still responded to a decrease in oxygen concentration, although here induction was about 10 times lower and the low oxygen response was gradually lost within 3 days. Introduced into a barley-soil microcosm, the biosensor could report decreasing oxygen concentrations in the rhizosphere for a 6-day period. When the water content in the microcosm was raised from 60% to 85% of field capacity, expression of the reporter gene was elevated about twofold above a basal level after 2 days of incubation, suggesting that a water content of 85% caused mild anoxia. Increased compaction of the soil was shown to have a faster and more dramatic effect on the expression of the oxygen reporter than soil water content alone, indicating that factors other than the water-filled pore space influenced the oxygen status of the soil. These experiments illustrate the utility of the biosensor for detecting low oxygen concentrations in the rhizosphere and other soil habitats.

Compressed Sensing Single-Breath-Hold CMR for Fast Quantification of LV Function, Volumes, and Mass.

OBJECTIVES: The purpose of this study was to compare a novel compressed sensing (CS)-based single-breath-hold multislice magnetic resonance cine technique with the standard multi-breath-hold technique for the assessment of left ventricular (LV) volumes and function. BACKGROUND: Cardiac magnetic resonance is generally accepted as the gold standard for LV volume and function assessment. LV function is 1 of the most important cardiac parameters for diagnosis and the monitoring of treatment effects. Recently, CS techniques have emerged as a means to accelerate data acquisition. METHODS: The prototype CS cine sequence acquires 3 long-axis and 4 short-axis cine loops in 1 single breath-hold (temporal/spatial resolution: 30 ms/1.5 × 1.5 mm(2); acceleration factor 11.0) to measure left ventricular ejection fraction (LVEFCS) as well as LV volumes and LV mass using LV model-based 4D software. For comparison, a conventional stack of multi-breath-hold cine images was acquired (temporal/spatial resolution 40 ms/1.2 × 1.6 mm(2)). As a reference for the left ventricular stroke volume (LVSV), aortic flow was measured by phase-contrast acquisition. RESULTS: In 94% of the 33 participants (12 volunteers: mean age 33 ± 7 years; 21 patients: mean age 63 ± 13 years with different LV pathologies), the image quality of the CS acquisitions was excellent. LVEFCS and LVEFstandard were similar (48.5 ± 15.9% vs. 49.8 ± 15.8%; p = 0.11; r = 0.96; slope 0.97; p < 0.00001). Agreement of LVSVCS with aortic flow was superior to that of LVSVstandard (overestimation vs. aortic flow: 5.6 ± 6.5 ml vs. 16.2 ± 11.7 ml, respectively; p = 0.012) with less variability (r = 0.91; p < 0.00001 for the CS technique vs. r = 0.71; p < 0.01 for the standard technique). The intraobserver and interobserver agreement for all CS parameters was good (slopes 0.93 to 1.06; r = 0.90 to 0.99). CONCLUSIONS: The results demonstrated the feasibility of applying the CS strategy to evaluate LV function and volumes with high accuracy in patients. The single-breath-hold CS strategy has the potential to replace the multi-breath-hold standard cardiac magnetic resonance technique.

GLUT2, glucose sensing and glucose homeostasis.

The glucose transporter isoform GLUT2 is expressed in liver, intestine, kidney and pancreatic islet beta cells, as well as in the central nervous system, in neurons, astrocytes and tanycytes. Physiological studies of genetically modified mice have revealed a role for GLUT2 in several regulatory mechanisms. In pancreatic beta cells, GLUT2 is required for glucose-stimulated insulin secretion. In hepatocytes, suppression of GLUT2 expression revealed the existence of an unsuspected glucose output pathway that may depend on a membrane traffic-dependent mechanism. GLUT2 expression is nevertheless required for the physiological control of glucose-sensitive genes, and its inactivation in the liver leads to impaired glucose-stimulated insulin secretion, revealing a liver-beta cell axis, which is likely to be dependent on bile acids controlling beta cell secretion capacity. In the nervous system, GLUT2-dependent glucose sensing controls feeding, thermoregulation and pancreatic islet cell mass and function, as well as sympathetic and parasympathetic activities. Electrophysiological and optogenetic techniques established that Glut2 (also known as Slc2a2)-expressing neurons of the nucleus tractus solitarius can be activated by hypoglycaemia to stimulate glucagon secretion. In humans, inactivating mutations in GLUT2 cause Fanconi-Bickel syndrome, which is characterised by hepatomegaly and kidney disease; defects in insulin secretion are rare in adult patients, but GLUT2 mutations cause transient neonatal diabetes. Genome-wide association studies have reported that GLUT2 variants increase the risks of fasting hyperglycaemia, transition to type 2 diabetes, hypercholesterolaemia and cardiovascular diseases. Individuals with a missense mutation in GLUT2 show preference for sugar-containing foods. We will discuss how studies in mice help interpret the role of GLUT2 in human physiology.

Sensing of glucose in the brain.

The brain, and in particular the hypothalamus and brainstem, have been recognized for decades as important centers for the homeostatic control of feeding, energy expenditure, and glucose homeostasis. These structures contain neurons and neuronal circuits that may be directly or indirectly activated or inhibited by glucose, lipids, or amino acids. The detection by neurons of these nutrient cues may become deregulated, and possibly cause metabolic diseases such as obesity and diabetes. Thus, there is a major interest in identifying these neurons, how they respond to nutrients, the neuronal circuits they form, and the physiological function they control. Here I will review some aspects of glucose sensing by the brain. The brain is responsive to both hyperglycemia and hypoglycemia, and the glucose sensing cells involved are distributed in several anatomical sites that are connected to each other. These eventually control the activity of the sympathetic or parasympathetic nervous system, which regulates the function of peripheral organs such as liver, white and brown fat, muscle, and pancreatic islets alpha and beta cells. There is now evidence for an extreme diversity in the sensing mechanisms used, and these will be reviewed.

The Quorum-Sensing Molecules Farnesol/Homoserine Lactone and Dodecanol Operate via Distinct Modes of Action in Candida albicans.

Living as a commensal, Candida albicans must adapt and respond to environmental cues generated by the mammalian host and by microbes comprising the natural flora. These signals have opposing effects on C. albicans, with host cues promoting the yeast-to-hyphal transition and bacteria-derived quorum-sensing molecules inhibiting hyphal development. Hyphal development is regulated through modulation of the cyclic AMP (cAMP)/protein kinase A (PKA) signaling pathway, and it has been postulated that quorum-sensing molecules can affect filamentation by inhibiting the cAMP pathway. Here, we show that both farnesol and 3-oxo-C(12)-homoserine lactone, a quorum-sensing molecule secreted by Pseudomonas aeruginosa, block hyphal development by affecting cAMP signaling; they both directly inhibited the activity of the Candida adenylyl cyclase, Cyr1p. In contrast, the 12-carbon alcohol dodecanol appeared to modulate hyphal development and the cAMP signaling pathway without directly affecting the activity of Cyr1p. Instead, we show that dodecanol exerted its effects through a mechanism involving the C. albicans hyphal repressor, Sfl1p. Deletion of SFL1 did not affect the response to farnesol but did interfere with the response to dodecanol. Therefore, quorum sensing in C. albicans is mediated via multiple mechanisms of action. Interestingly, our experiments raise the possibility that the Burkholderia cenocepacia diffusible signal factor, BDSF, also mediates its effects via Sfl1p, suggesting that dodecanol's mode of action, but not farnesol or 3-oxo-C(12)-homoserine lactone, may be used by other quorum-sensing molecules.

Plasma membrane cyclic nucleotide gated calcium channels control land plant thermal sensing and acquired thermotolerance.

Typically at dawn on a hot summer day, land plants need precise molecular thermometers to sense harmless increments in the ambient temperature to induce a timely heat shock response (HSR) and accumulate protective heat shock proteins in anticipation of harmful temperatures at mid-day. Here, we found that the cyclic nucleotide gated calcium channel (CNGC) CNGCb gene from Physcomitrella patens and its Arabidopsis thaliana ortholog CNGC2, encode a component of cyclic nucleotide gated Ca(2+) channels that act as the primary thermosensors of land plant cells. Disruption of CNGCb or CNGC2 produced a hyper-thermosensitive phenotype, giving rise to an HSR and acquired thermotolerance at significantly milder heat-priming treatments than in wild-type plants. In an aequorin-expressing moss, CNGCb loss-of-function caused a hyper-thermoresponsive Ca(2+) influx and altered Ca(2+) signaling. Patch clamp recordings on moss protoplasts showed the presence of three distinct thermoresponsive Ca(2+) channels in wild-type cells. Deletion of CNGCb led to a total absence of one and increased the open probability of the remaining two thermoresponsive Ca(2+) channels. Thus, CNGC2 and CNGCb are expected to form heteromeric Ca(2+) channels with other related CNGCs. These channels in the plasma membrane respond to increments in the ambient temperature by triggering an optimal HSR, leading to the onset of plant acquired thermotolerance.

Role of prostacyclin versus peroxisome proliferator-activated receptor beta receptors in prostacyclin sensing by lung fibroblasts.

Prostacyclin and its mimetics are used therapeutically for the treatment of pulmonary hypertension. These drugs act via cell surface prostacyclin receptors (IP receptors); however, some of them can also activate the nuclear receptor peroxisome proliferator-activated receptor beta (PPARbeta). We examined the possibility that PPARbeta is a therapeutic target for the treatment of pulmonary hypertension. Using the newly approved (for pulmonary hypertension) prostacyclin mimetic treprostinil sodium, reporter gene assays for PPARbeta activation and measurement of lung fibroblast proliferation were analyzed. Treprostinil sodium was found to activate PPARbeta in reporter gene assays and to inhibit proliferation of human lung fibroblasts at concentrations consistent with an effect on PPARs but not on IP receptors. The effects of treprostinil sodium on human lung cell proliferation are mimicked by those of the highly selective PPARbeta ligand GW0742. There are no receptor antagonists for PPARbeta or for IP receptors, but by using lung fibroblasts cultured from mice lacking PPARbeta (PPARbeta-/-) or IP (IP-/-), we demonstrate that the antiproliferative effects of treprostinil sodium are mediated by PPARbeta and not IP in lung fibroblasts. These observations suggest that some of the local, longer-term benefits of treprostinil sodium on reducing the remodeling associated with pulmonary hypertension may be mediated by PPARbeta. This study is the first to identify PPARbeta as a potential therapeutic target for the treatment of pulmonary hypertension, which is important because orally active PPARbeta ligands have been developed for the treatment of dyslipidemia.

Standardisation of 18F by a coincidence method using full solid angle detectors.

A solution of (18)F was standardised with a 4pibeta-4pigamma coincidence counting system in which the beta detector is a one-inch diameter cylindrical UPS89 plastic scintillator, positioned at the bottom of a well-type 5''x5'' NaI(Tl) gamma-ray detector. Almost full detection efficiency-which was varied downwards electronically-was achieved in the beta-channel. Aliquots of this (18)F solution were also measured using 4pigamma NaI(Tl) integral counting and Monte Carlo calculated efficiencies as well as the CIEMAT-NIST method. Secondary measurements of the same solution were also performed with an IG11 ionisation chamber whose equivalent activity is traceable to the Système International de Référence through the contribution IRA-METAS made to it in 2001; IRA's degree of equivalence was found to be close to the key comparison reference value (KCRV). The (18)F activity predicted by this coincidence system agrees closely with the ionisation chamber measurement and is compatible within one standard deviation of the other primary measurements. This work demonstrates that our new coincidence system can standardise short-lived radionuclides used in nuclear medicine.

Intercomparison of the response of different photon and neutron detectors around a spent fuel cask

An intercomparison of the response of different photon and neutron detectors was performed in several measurement positions around a spent fuel cask (type TN 12/2B) filled with 4 MOX and 8 UO2 15 x 15 PWR fuel assemblies at the nuclear power plant Gosgen (KKG) in Switzerland. The instruments used in the study were both active and passive, photon and neutron detectors calibrated either for ambient or personal dose equivalent. The aim of the measurement campaign was to compare the responses of the radiation instruments to routinely used detectors. It has been shown that especially the indications of the neutron detectors are strongly dependent on the neutron spectra around the cask due to their different energy responses. However, routinely used active photon and neutron detectors were shown to be reliable instruments. (C) 2012 Elsevier Ltd. All rights reserved.

Schistosomiasis risk mapping in the state of Minas Gerais, Brazil, using a decision tree approach, remote sensing data and sociological indicators

Schistosomiasis mansoni is not just a physical disease, but is related to social and behavioural factors as well. Snails of the Biomphalaria genus are an intermediate host for Schistosoma mansoni and infect humans through water. The objective of this study is to classify the risk of schistosomiasis in the state of Minas Gerais (MG). We focus on socioeconomic and demographic features, basic sanitation features, the presence of accumulated water bodies, dense vegetation in the summer and winter seasons and related terrain characteristics. We draw on the decision tree approach to infection risk modelling and mapping. The model robustness was properly verified. The main variables that were selected by the procedure included the terrain's water accumulation capacity, temperature extremes and the Human Development Index. In addition, the model was used to generate two maps, one that included risk classification for the entire of MG and another that included classification errors. The resulting map was 62.9% accurate.

Acute oxygen sensing in heme oxygenase-2 null mice.

Hemeoxygenase-2 (HO-2) is an antioxidant enzyme that can modulate recombinant maxi-K(+) channels and has been proposed to be the acute O(2) sensor in the carotid body (CB). We have tested the physiological contribution of this enzyme to O(2) sensing using HO-2 null mice. HO-2 deficiency leads to a CB phenotype characterized by organ growth and alteration in the expression of stress-dependent genes, including the maxi-K(+) channel alpha-subunit. However, sensitivity to hypoxia of CB is remarkably similar in HO-2 null animals and their control littermates. Moreover, the response to hypoxia in mouse and rat CB cells was maintained after blockade of maxi-K(+) channels with iberiotoxin. Hypoxia responsiveness of the adrenal medulla (AM) (another acutely responding O(2)-sensitive organ) was also unaltered by HO-2 deficiency. Our data suggest that redox disregulation resulting from HO-2 deficiency affects maxi-K(+) channel gene expression but it does not alter the intrinsic O(2) sensitivity of CB or AM cells. Therefore, HO-2 is not a universally used acute O(2) sensor.

Negative control of quorum sensing by RpoN (sigma54) in Pseudomonas aeruginosa PAO1.

In Pseudomonas aeruginosa PAO1, the expression of several virulence factors such as elastase, rhamnolipids, and hydrogen cyanide depends on quorum-sensing regulation, which involves the lasRI and rhlRI systems controlled by N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone, respectively, as signal molecules. In rpoN mutants lacking the transcription factor sigma(54), the expression of the lasR and lasI genes was elevated at low cell densities, whereas expression of the rhlR and rhlI genes was markedly enhanced throughout growth by comparison with the wild type and the complemented mutant strains. As a consequence, the rpoN mutants had elevated levels of both signal molecules and overexpressed the biosynthetic genes for elastase, rhamnolipids, and hydrogen cyanide. The quorum-sensing regulatory protein QscR was not involved in the negative control exerted by RpoN. By contrast, in an rpoN mutant, the expression of the gacA global regulatory gene was significantly increased during the entire growth cycle, whereas another global regulatory gene, vfr, was downregulated at high cell densities. In conclusion, it appears that GacA levels play an important role, probably indirectly, in the RpoN-dependent modulation of the quorum-sensing machinery of P. aeruginosa.

Self-Navigation with Compressed Sensing for 2D Translational Motion Correction in Free-Breathing Coronary MRI: A Feasibility Study.

PURPOSE: Respiratory motion correction remains a challenge in coronary magnetic resonance imaging (MRI) and current techniques, such as navigator gating, suffer from sub-optimal scan efficiency and ease-of-use. To overcome these limitations, an image-based self-navigation technique is proposed that uses "sub-images" and compressed sensing (CS) to obtain translational motion correction in 2D. The method was preliminarily implemented as a 2D technique and tested for feasibility for targeted coronary imaging. METHODS: During a 2D segmented radial k-space data acquisition, heavily undersampled sub-images were reconstructed from the readouts collected during each cardiac cycle. These sub-images may then be used for respiratory self-navigation. Alternatively, a CS reconstruction may be used to create these sub-images, so as to partially compensate for the heavy undersampling. Both approaches were quantitatively assessed using simulations and in vivo studies, and the resulting self-navigation strategies were then compared to conventional navigator gating. RESULTS: Sub-images reconstructed using CS showed a lower artifact level than sub-images reconstructed without CS. As a result, the final image quality was significantly better when using CS-assisted self-navigation as opposed to the non-CS approach. Moreover, while both self-navigation techniques led to a 69% scan time reduction (as compared to navigator gating), there was no significant difference in image quality between the CS-assisted self-navigation technique and conventional navigator gating, despite the significant decrease in scan time. CONCLUSIONS: CS-assisted self-navigation using 2D translational motion correction demonstrated feasibility of producing coronary MRA data with image quality comparable to that obtained with conventional navigator gating, and does so without the use of additional acquisitions or motion modeling, while still allowing for 100% scan efficiency and an improved ease-of-use. In conclusion, compressed sensing may become a critical adjunct for 2D translational motion correction in free-breathing cardiac imaging with high spatial resolution. An expansion to modern 3D approaches is now warranted.